Baicalein attenuates bleomycin-induced pulmonary fibrosis via endothelial Piezo1-associated Ca2+/calpain-MAPK signaling and EndMT-associated remodeling.

Pulmonary fibrosis is a progressive fibrotic lung disorder in which chemical injury, inflammation, extracellular matrix deposition, and endothelial dysfunction converge to remodel lung architecture. Baicalein, a chemically defined flavonoid, has reported anti-inflammatory and antifibrotic activity, but the endothelial mechanotransduction events linked to its effects in bleomycin-induced fibrosis remain insufficiently defined. Here, we evaluated whether baicalein modulates endothelial Piezo1-associated signaling during experimental pulmonary fibrosis. A bleomycin-induced mouse model, endothelial cell-specific Piezo1 knockout mice, primary mouse pulmonary microvascular endothelial cells (PMECs), and HUVEC-based mechanistic assays were used to examine lung injury, collagen accumulation, endothelial-to-mesenchymal transition (EndMT), calcium influx, calpain activity, and MAPK activation. Baicalein reduced bleomycin-associated lung inflammation, collagen deposition, hydroxyproline accumulation, and EndMT-associated marker changes. Mechanistically, baicalein lowered Piezo1 expression and Piezo1-associated Ca2+ influx in endothelial cells, accompanied by reduced calpain activity and decreased phosphorylation of p38, ERK, and JNK. Endothelial Piezo1 deletion attenuated bleomycin-induced fibrotic remodeling and partially blunted the additional protective response to baicalein, supporting the functional involvement of endothelial Piezo1 while not excluding Piezo1-independent effects. These findings suggest that baicalein alleviates experimental pulmonary fibrosis, at least in part, by modulating the endothelial Piezo1/Ca2+/calpain-MAPK signaling axis and suppressing EndMT-associated changes. The data support endothelial mechanotransduction as a pharmacologically relevant node in fibrotic lung injury, but direct baicalein-Piezo1 binding, pathway epistasis, pharmacokinetics, and long-term safety require further validation.